The invention relates to an information bearing card such as a credit card or an identification card and a method of making the same.
Credit cards are normally made of a standard plastic substrate of PVC (polyvinylchloride) on which information is printed, embossed or stored in the form of a magnetic strip or the like. Unlike paper which can be watermarked and manufactured with various modifications which make its identification and origin reasonably and sometimes definitely certain, all PVC is very much the same and its origin cannot be differentiated even under laboratory analysis.
Forgery and illegal use of credit cards is a multimillion dollar industry within the United States. Embossing plastic sheets to resemble valid credit cards is not technically difficult and such credit cards are substantially indistinguishable from valid cards. Discovery of the illegal use normally occurs only when someone whose valid card has the same number as the illegal card complains that he has received a bill for items which he did not purchase. Typically, this occurs only some weeks or months after the illegal use by which time the counterfeiter has ceased use of the card and began use of another illegal card. Furthermore, even when the illegal user of the card is apprehended, it is virtually impossible to trace the card to the manufacturer thereof in a way which would permit prosecution of that individual or entity.
Various plastic manufacturers have attempted to personalize their product with the inclusion of bits of foreign matter. Bronze powder and the like have been introduced into the PVC. While of some benefit, this approach is not a complete solution since sophisticated counterfeiters have access to similar foreign matter and can simply adjust their processes to add the same material.
Another approach has been to include within the card or to add to the card a diffraction grating, preferably a hologram. The hologram can be actually embodied in the card, for example as shown in U.S. Pat. No. 3,620,590, or attached thereto in the form of a sticker. Such a hologram is difficult for counterfeiters to duplicate and provides a simple visual check of the validity of a card presented for credit. Even should counterfeiters be able to produce a holographic image resembling that on the card, the hologram can be made to have unique spectral characteristics which cannot be readily duplicated.
However, such holograms forming part of a credit card present a number of disadvantages. First, the use of a sticker hologram forming an image, or even a colorful pattern, is expensive and incorporating a holographic or diffraction pattern within the card is even more expensive. The stickers or holograms can be removed from valid cards or fake holograms added so that their potential for use illegally still exists.
The present invention relates to a unique information bearing card and method of forming the same. According to the present invention, a diffraction grating, for example a hologram embossed upon a polyester or paper sheet or the like, is shredded into pieces and distributed, preferably randomly, in a conventional plastic sheet of PVC or at the head box of the paper manufacturer. The pieces of the diffraction grating each reflect light having unique optical characteristics in accordance with the way that the diffraction grating is formed. Not only does this provide a simple visual check to see if a card comes from an authorized source, but the light reflected can be analyzed for example by spectrography, to determine quickly, easily and with accuracy the source or the manufacturer of the plastic blanks. Moreover, since the pieces are distributed in the card, if one or more of these should become obscured for any reason, the remaining pieces will still provide the same response to incident light.
The pieces of the diffraction grating can be added to the PVC sheets in at least two different ways. After shredding, the pieces can be simply mixed with the dough-like substance resulting from mixing of powdered resins and liquid chemicals called a "pig". This pig is conventionally then rolled into sheets and cut into credit card blanks. Alternatively, the shredded pieces can simply be sprinkled into the sheet as it is rolled so that the pieces are lodged near the surface on one side of the sheet.
Alternatively the pieces of diffraction grating can be incorporated in some other substrate, such as paper, by adding in the same way during manufacture.
Other objects and purposes of the invention will be clear from the following detailed description of the drawings.